The present invention is directed to a shifting apparatus for a bicycle and, more particularly, to a shifting apparatus having first and second levers which cooperate with a take-up mechanism for alternately pulling and releasing a speed change member for changing gears of a bicycle transmission.
A conventional shifting apparatus of the above type is described in Japanese Patent Application Kokai No. 5-319355. Such a shifting apparatus is equipped with two speed-change levers which are capable of automatically returning to a start position. The speed-change wire is operated in the take-up direction by a thumb-operated speed-change lever, and the speed change wire is operated in the pay-out direction by a speed-change lever normally operated by an index finger. These two speed-change levers are supported so that the levers can pivot together about the vertical axis of the bicycle body. The finger-contact operating part of the speed-change lever which is operated with the thumb pivots in the forward-backward direction underneath the handlebar. This lever is arranged so that, when the operating part pivots toward the handlebar, the speed-change wire is operated in the take-up direction. The finger-contact operating part of the speed-change lever which is operated with the index finger also pivots in the forward-backward direction underneath the handlebar. This lever is similarly arranged so that, when the operating part pivots toward the handlebar, the speed-change wire is operated in the pay-out direction.
If the respective directions of operating movement of the finger-contact operating parts of the two speed-change levers in the conventional speed-change operating mechanism are considered, it will be understood that the finger-contact operating part of the speed-change lever which is operated with the index finger moves in the same manner as the trigger in a pistol. Thus, the operating part can be operated by a relatively natural movement of the index finger. However, the finger-contact operating part of the speed-change lever which is operated with the thumb is operated by pushing the finger-contact operating part toward the handlebar (i.e., toward the front underneath the handlebar). As a result, especially in the initial stage of operation, it is necessary to push the finger-contact operating part toward the front with the palm of the hand slightly removed from the grip part of the handlebar. When the shifting apparatus is mounted to a mountain bike, for example, which is used for riding in rough off-road areas, considerable difficulty is involved in the speed-change operation performed with the thumb during riding.